Origin of roughening in epitaxial growth of silicon on Si(001) and Ge(001)surfaces

It is shown that the formation of (2 x 1) reconstructed islands during the growth of Si on Si(0 0 1) and Ge(0 0 1) surfaces at moderate temperatures a nd the consequent anisotropic diffusion and sticking lead to roughening. As Si islands nucleate and expand, the dimer rows in neighboring rows need no t, in general, align with each other. An antiphase boundary (APB) will be f ound if two growing islands meet, but their internal dimer rows are not in the same registry. One type of APB runs perpendicular to the substrate rows , whereas the other runs along the substrate rows. As has been pointed out by Harriers et al. [J. Vac. Sci. Technol. A 8 (1990) 195] this first type o f APB is a preferential center for nucleation of next layer islands and thu s naturally leads to roughening. Here we show that the other type of APB le ads, in combination with the anisotropy in sticking and diffusion of dimers , to the formation of long B-type double layer steps and narrow trenches. W e argue that it is the kinetic suppression of filling of these trenches and not, as previously suggested the existence of step edge barrier for the do uble layer step edge that leads to roughening. (C) 2001 Elsevier Science B. V. All rights reserved.